Ultrasonic diagnostic apparatus

Abstract

Disclosed is a celiac diagnostic apparatus in which the characteristics of a filter for filtering a wave reflected by a tissue inside an object are made steep, and an ultrasonic wave capable of making a high-accuracy diagnosis for the object is used. C1, C2, and C3 are constituted using variable capacitance diodes. Three LC filters, i.e., an LC filter constituted by L1 and C1, an LC filter constituted by L2 and C2, and an LC filter constituted by L3 and C3 are serially connected to constitute the filter, whose cutoff characteristics is still practical even when the cutoff frequency exceeds 20 MHz.

What is claimed is: 
     
       1. An ultrasonic apparatus for transmitting an ultrasonic wave to an object to assist in making a diagnosis for the object on the basis of a reflected wave from the transmitted wave, comprising: transmission means for transmitting the ultrasonic wave to the object: reception means for receiving the reflected wave by the object and converting the reflected wave into an electrical signal;   filter means for filtering the electrical signal; and   control means for controlling a filter characteristic of said filter means, wherein said filter means includes at least two connected LC filters, each including a capacitor including a variable capacitance diode and an inductor,   said control means adjusts a capacitance of at least one of the variable capacitance diodes in accordance with a depth to the object so as to control the filter characteristic of said filter means,   a value of the capacitor including the variable capacitance diode is optimized around a lower limit and an upper limit within a variable range of a cutoff frequency of said filter means,   a value of the inductor is opimizied around a median within the variable range, and   a high-frequency side of the cutoff frequency is variable within a range of 20 MHZ or more.       
     
     
       2. The apparatus according to claim 1, wherein said control means decreases a cutoff frequency of a high-frequency side in said filter means as a depth to the observed object increases. 
     
     
       3. The apparatus according to claim 1, wherein said control means decreases a cutoff frequency of a high-frequency side in said filter means on the basis of an elapsed time from a start of transmitting the ultrasonic wave to the object. 
     
     
       4. The apparatus according to claim 1, wherein said filter means is a bandpass filter, and a flat characteristic of a passband in the bandpass filter falls within 0.1 dB. 
     
     
       5. The apparatus according to claim 1, further comprising imaging means for generating image information on the basis of the electrical signal filtered by said filter means. 
     
     
       6. An ultrasonic apparatus for transmitting an ultrasonic wave to an object to assist in making a diagnosis for the object on the basis of a reflected wave from the transmitted wave, comprising: catheter incorporating transmitting means for generating an ultrasonic wave and transmitting the ultrasonic wave to the object;   reception means for receiving an ultrasonic wave reflected from the object and converting the reflected wave into an electrical signal;   filter means for filtering the electrical signal; and   control means for controlling a filter characteristic of said filter means, wherein said control means keeps the filter characteristic almost constant on the reflected wave from inside of a body cavity where said catheter is inserted, while changing the filter characteristic on the reflected wave from outside of the body cavity in accordance with a depth to the observed object from a portion near a wall tissue of the body cavity.     
     
     
       7. The apparatus according to claim 6, wherein, as the observation depth from the portion near the wall tissue of the body cavity increases, said control means decreases a cutoff frequency of a high-frequency side in said filter means on the reflected wave from the outside of the body cavity where said catheter is inserted. 
     
     
       8. The apparatus according to claim 6, wherein, on the basis of reception of a reflected wave, exceeding a predetermined level, of waves reflected by the object, after the reception of the reflected wave, said control means decreases a cutoff frequency of a high-frequency side in said filter means as the observation depth from the tissue inside the object associated with the reflected wave increases. 
     
     
       9. The apparatus according to claim 6, wherein said control means decreases a cutoff frequency of a high-frequency side in said filter means in accordance with an elapsed time from reception of a reflected wave, exceeding a predetermined level, of waves reflected by the object. 
     
     
       10. The apparatus according to claim 6, wherein said filter means comprises an LC filter including a variable capacitance diode, and said control means adjusts a capacitance of the variable capacitance diode so as to change the filter characteristic. 
     
     
       11. The apparatus according to claim 6, wherein said filter means includes at least two connected LC filters, each including a variable capacitance diode, and said control means adjusts a capacitance of at least one of the variable capacitance diodes so as to change the filter characteristic. 
     
     
       12. The apparatus according to claim 11, wherein said filter means is a bandpass filter, a cutoff frequency of a high-frequency side in the bandpass filter is variable within a range of 20 MHZ or more, and a flat characteristic of a passband in the bandpass filter falls within 0.1 dB. 
     
     
       13. The apparatus according to claim 6, further comprising imaging means for generating image information on the basis of the electrical signal filtered by said filter means.